1. Field of the Invention
The present invention relates to an exposure apparatus which is adapted to expose a material to be exposed to parallel lights in a manner that the material or the parallel lights are moved and, more particularly, to a parallel light moving type exposure apparatus which is capable of obtaining a uniform cumulated amount of light and a wide area of irradiation.
2. Description of the Prior Art
Where a work such as a printed board, or printed circuit board is exposed to and baked by lights, it is necessary that an image of a printing mask is reproduced with high precision onto the work. To this end, it is preferable to use an exposure apparatus which uses parallel lights. Conventionally, an exposure apparatus was such that, as shown in FIG. 4A, a large-depth parabolic reflector 101 is employed within which a point light source 103 is provided together with a light-shielding member 102 which is located right beneath the light source 103. The light-shielding member 102 is made spherical to remove the direct irradiation by reflection or absorption so as to obtain only parallel lights. By that shadow of the light-shielding member 102 which is necessarily produced at that time on an irradiation plane, this irradiation plane is limited and any point on a material to be exposed such as a mask or a work which passes therethrough is exposed to light always with a specified amount of light.
The above-mentioned old technique, however, had the following problems. Firstly, since the light-shielding member 102 utilizes a reflection, an irregular reflection is produced due to, for example, the light source 103 being not an ideal point light source 103. It disturbs the parallel lights. For this reason, the practical use was impossible. Secondly, the light-shielding member 102 adapted for shielding the direct irradiation in an optimum manner and obtaining an optimum cumulated amount of light is not easy to design or adjust because its size, shape and a distance as measured from the light source affect each other in a complicated manner. Thirdly, the point light source 103 is actually not a point light source but is of some largeness or of some depth, so that the lights obtained are not complete parallel lights. For this reason, in order to obtain a precise area of exposure, it was necessary to dispose the light-shielding member at a position closer to that of the material to be exposed. This results in a decrease in area of the zone in which the direct irradiation is shielded. In order to avoid the material from receiving the direct irradiation, it was necessary to dispose the material to be exposed at a position farther away from the position of the light-shielding member 102, and/or to make the light-shielding member 102 larger in size. These countermeasures, however, cause a decrease in the utilizing efficiency with which the light source 103 is utilized. Fourthly and finally, the decrease in the light-source utilizing efficiency made it necessary to use a large-depth parabolic reflector. The use of such a large-depth parabolic reflector, however, results in an illumination distribution in which the light intensity is greatly uneven, as shown in FIG. 4. This makes it difficult to calculate the cumulated amount of light and, at the same time, to make the usable exposure area narrow.